Explain what "dead reckoning" is in navigation.

Dead reckoning is a fundamental navigation technique used to estimate a vessel's current position based on its previous location, speed, and course over time. This method involves calculating the distance traveled from a known point and determining the vessel's position by projecting its course forward. It is essential for navigators, especially when visual landmarks are not available or when navigating in open waters.

In this method, navigators rely on accurate records of course direction and speed to calculate the new position after a certain duration. This process creates a path or vector, allowing them to predict where the vessel is likely to be at a given time. While dead reckoning can be very effective, it does have limitations, such as accumulation of errors due to factors like current, wind, or changes in course, which can lead to discrepancies in the estimated position.

The other methods presented do not capture the essence of dead reckoning accurately: estimating speed alone does not provide a complete navigation solution, land navigation techniques are specific to terrestrial conditions and not applicable to maritime navigation, and measuring the accuracy of navigational aids pertains more to evaluating external assistance rather than calculating a position based on historical data. Thus, the definition provided by the correct answer aptly encompasses the core concept of dead reckoning.